The celebrity couple named their youngest son Hayes, keeping in line with his two older sisters, Honor and Haven.
"Hayes Alba Warren 12/31/17 Best gift to ring in the New Year!!" Alba wrote on Instagram. "Cash and I feel so blessed. Haven and Honor are already obsessed with their new baby bro. #familyof5."
Warren followed suit with an Instagram post of his own praising Hayes and his mother.
"Hayes Alba Warren: You sure know how to ring in the new year!" he wrote. "You showed up a few days early but we couldn't be any happier. Your Mamma is the strongest woman I know ... you're so lucky to have her by your side. You have two amazing sisters who already adore you and I know you'll be thankful to have them guide the way. On your first day of life, I promise to love you, to cherish you, and to provide you with a sandbox full of dreams to explore. Welcome to the family my sweet baby Hayes! 12/31/2017"
Congratulations to the happy family!